Ammonium nitrate-hexamethylene-tetramine adduct



Jan. 19, 1965 w. E. GORDON 3,166,555

AMMONIUM NITRATEl-I-IEXAMETI-IYLENETETRAMINE ADDUCT Filed June 6, 1962 2Sheets-Sheet 1 o INITIAL CONCENTRATION OF HEXAHINE D INITIALCONCENTRATION OF M- NITRATE son 1 SOLIIBILITY 3, (g/IOOg water) 6 mum:I: 20 no so so 100 TEMPERATURE (C) FIGURE 1 INVENTOR. WILLIAM E. GORDONATTORNEY Jan. 19, 1965 w. E. GORDON AMMONIUM NITRATE-HEXAMETHYLENETETRAMINE ADDUCT 2 Sheets-Sheet 2 Filed June 6, 1962n22 6250mm 88 I INVENTOR. WILLIAM E. GORDON ATTORNEY 8 3 (maaaaa)HDNVUIWSNVHL United States Patent dice 3,166,555 AMWIONIUM.NI'I'RATE-HEXAMETHYLENE- TETRAMINE ADDUCT William E. Gordon, Bethesda,Md., assignor to Arthur 1).

Little, Inc, Cambridge, Mass, a corporation of Massachusetts Filed June6, 1962, Ser. No. 200,439

3 Claims. (Cl. 260-2485) been useful only as blasting agents, asdistinguished from stick dynarnites, i.e., cartridge explosives, unlessingredients of the molecular explosive type such as nitroglycerin areincluded in the formulations. Blasting agents require a large diametercharge and must be initiated with a high explosive primer. A cartridgeexplosive, on the other hand, is a stick-type charge that has a smalldiameter and is detonable by means of a No. 6 or a No. 8 blasting cap;In the trade, cartridge explosives are simply called dynamite.Throughout this specification the term cap sensitive cartridge explosiveis intended to designate an explosive that may be detonated by a No. 6or a No. 8 blasting cap in an eight-inch paper cartridge havingadiameter of about 1.25 inches.

The primary object of this invention is to provide im proved explosiveformulations comprising ammonium nitrate and hexamethylenetetraminewhich not only may be used as blasting agents but also are eminentlysuitable as cap sensitive cartridge explosives.

Another object of this invention is to provide methods of making theafore-mentioned improved explosive formulations. V

In accordance with my invention, I have discovered an adduct ofhexamethylenetetramine and ammonium nitrate-which significantlyincreases the cap sensitivity of explosive formulations. This adduct hasthe empirical formula (CH N 2NH,N0

Other objects and advantages of my invention will become apparent fromthe following description of this invention, and from the accompanyingdrawing in which:

FIGURE 1 is a plot of the solubilities of ammonium nitrate andhexamethylenetetramine in water at various temperatures.

FIGURE 2 is the infrared spectrogram of the adduct of ammonium nitrateand hexamethylenetetramine of this invention.

. I. ADDUCT: METHODS OF PREPARATION A. Crystallization from watersolution' I prefer to prepare the adduct of this invention bycrystallization from an aqueous solution of hexamethylenetetramine andammonium nitrate. However, it is essential to the successful productionof the adduct by this method to conduct the crystallization under thefollowing two conditions.

Patented Jan. 19, 1965 Secondly, crystallization of the adduct iseffected by removal of the water at a temperature below ahout 40 C., andpreferably below 30 C. Such removal is preferably accomplished by airdrying, that is, by evaporating the water in a stream of air passingover or through the! aqueous solution. However, the water may beremoved;

by other conventional means such as under vacuum, by.

spray drying, by azeotropic distillation with a solvent, etc provided,always, that the temperature be maintained below 40 C. I

By way of example of the preferred method of preparation, 700 gramsof'hexamethylenetetramine and 800' grams of ammonium nitrate weredissolved in 700 grams of water at 20 C. The solution was placed inevapo-' rating dishes and a stream of air'was passed over the;

surface of the solution. After about 25 hours, virtually all the waterwas evaporated, leaving a heavy slush. The latter was filtered through aBiichner funnel and the crystals pressed with a rubber darn; rinsedtwice with water-free acetone; and then again pressed to remove theacetone. The crystals were removed from the Biichner, transferred tolarge filter papers and allowed to dry. The crystals were established tobe pure adduct, as will be later set forth.

Attempts to prepare the adduct in the manner set forth in the foregoingexample failed when the molar ratio of the hexamethylenetetramine andammonium nitrate was substantially different from one to two. Forexample, when the molar ratio was one to ten (the ratio corresponding toan oxygen-balanced system of oxidizerand fuel), no adduct wasprecipitated. The ammonium nitrate crystallized separately leaving thehexamethylenetetramine in the mother liquor. However, if thisoxygenbalanced system of hexamethylenetetramine and ammonium nitrate isprepared by taking the solution to complete dryness by evaporation atroom temperature, then the adduct can be detected in small quantities byX-ray diffraction techniques. Similarly, if an intimate mixture ofhexamethylenetetramine and ammonium nitrate is allowed to stand forseveral hours in the presence of a small amount of adsorbed moisture,adduct can be detected.

Attempts to prepare the adduct by crystallization at a temperature above40 C. failed, even though the molar ratio was one to two. For example, asolution of the two components in the proper ratio was prepared whichwas saturated with respect to the hexamethylenetetramine at 70 C. Uponremoval of the water by vacuum drying at 70 C, crystals of thehexamethylenetetramine precipitated, but no adduct was detected by X-raydiffraction of the crystalline precipitate, and the melting point wasthat of the hexamethylenetetramine.

Reference to FIGURE 1 of the drawing suggests a possible explanation ofthe above-described behavior. It

will be noted that the solubility of ammonium nitrate in wateraccelerates rapidly with rising temperature, while that 'of thehexamethylenetetramine actually declines. The circle and the squarerepresent the initial concentrations of the hexamethylenetetramine andthe ammonium nitrate, respectively, used in adduct preparation. At theseconcentrations the two components precipitate together, thus giving theadduct an opportunity to form. However, at higher temperatures, or withwidely disparate concentrations, one component crystallizespreferentially to the exclusion of the other.

B. Crystallization fr'om melts The adduct may also be made without waterby melting the two ingredients hexamethylenetetramine and ammoniumnitrate in the proper molar ratio, i.e., one to two, and

then quickly cooling the molten mixture. The adduct is successfully madeprovided that as soon as the mixture is molten, it is quickly cooled.Otherwise, the adduct decomposes as a result of exposure to the elevatedtemperatures. In my copending application Serial No. 146,944, I showedhow the adduct' is formed even when an oxyg en-balanced mixture ofhexamethylenetetramine and ammonium nitrate is melted and then rapidlycooled. It was in such a product that I first discovered the existenceof the adduct. However, the separation of the adduct in pure form fromthat product is diiiicult. Acc ordingly, I prefer when making the adductby the melting process to employ the proper molar ratio, but still touse the hot melting roll and the cooled crystallizing roll as describedin the aforementioned application.

By Way of example of the melting process, the required proportions ofhexamethylenetetramine and ammonium nitrate (1:2) were thoroughly mixed,and then hammermilled. The resulting finely ground mixture was passedonto a hot metal roll which was maintained at a temperature of about 160C. and which revolved at about one rpm. ;The molten material was thenpassed onto a counter-rotating cold metal roll which was maintained atabout C. where the'molten material was congealed,

in the form of flakes. The latter consisted essentially of.

pure crystals of adduct.

II. ADDUCT: STRUCTURE A. X-ray diflraction pattern The fact that thecrystals obtained as described above have a distinct crystallinestructure different from either hexamethylenetetramine or ammoniumnitrate was established by the use of X-ray diffraction techniques. Thefollowing table gives in approximate terms the relative intensities I/Iof the adduct for different values of the interplanar spacings expressedin angstrom units, d(A.).

TAB LE I From this table it will be noted that the major peaks are at4.07 A., 4.45 A., and 5.27 A.

B. Infrared analysis III. ADDUCT: PROPERTIES A. Empirical formula: (CH N-2NH NO B. Solubility in water: .Very soluble in hot or cold water.At'10 C. about 220 grams will dissolve in 100 grams of water. p C.Solubility in organic solvents: Sparingly soluble in acetone, ethylalcohol and ether.

D. Melting point: About 122 C. (completely liquid by 132 C.). Prolongedheating above this temperature vturns the melt yellowish. After eighteenhours 1 at 125 C., the melt becomes a viscous tar-like liquid with astrong amine odor. Before reaching this state, fumes of ammonia aregiven off.

E. Color: Colorless and transparent as individual crystal.

F. Explosive properties: The adduct per se is a weak molecularexplosive. It is heavily fuel-rich relative to oxygen balance. It haslittle sensitivity but is detonable with adequate boostering in properconfinement I and diameter. In 2.0 inchdiameter, 0.5 inch thick steel'walled tubes and boostered with a 25-gram tetryl-pel' let, adduct in ahammermilled form has a detonation velocity of 10,400 f./s. at a densityof 0.84 g./cc.

IV. ADDUCT: EXPLOSIVE FORMULATIONS Adduct was blended with ammoniumnitrate prills in the proportion of.1 to 4.02 parts by weightrespectively. This proportion produces an oxygen-balanced formulation.The resulting mixture was tumbled to assure com plete mixing and thenpassed through a hammermill. Sieve analysis gave 74 percent of thematerial through 200 mesh. Samples of the product were exploded incartridges of differentsizes. The detonation velocity for each explosionwas determined in conventional fashion. The data obtained are presentedin the following Table II.

TABLE II.EXPLOSIVE DATA Cartridge Size (in) Densit Primer Velocity gJcc.(f./s.)

1.25 x 8 0 No. GEBO 1 18, 300

1.0x8 0. 95 No.6 EBC 11,900

0.75 x10 0. 95 No. 6 EBO 10,400

1 N0. 6 Electric Blasting Cap.

From the above, it will be seen that the blend of adduct and ammoniumnitrate is a cap sensitive stick explosive. In general, it has areaction zone length, a of about 0.27 inch and a critical diameter, d=0.50 inch (appr Its velocity in 1.25 inch diameter is about 13,300 f-Pat 0.95 density. Its gap sensitivity is about 3 inches.

Oxygen-balanced explosives containing the adduct of my invention may beprepared by the method described in the aforesaid application Serial No.146,944, that is, by melting a mixture of ammonium nitrate andhexamethylenetetramine in oxygen balanced proportions, and thereafterrapidly chilling'the'molten mass. By rapidly chilling the melt, crystalsof ammonium nitrate are obtained that have a maximum dimension notexceeding microns. At least a portion of these crystals is enveloped ina continuous crystalline matrixoftheadduct and any Ihexamethylenetetramine which may not have formed'adduct. X-raydiffraction tests performed on the resulting products showed a prominentX-ray diffraction pattern peak at about 4.45 A. This peak is notassociated either with hexamethylenetetramine or ammonium nitrate. Thedensity of explosives prepared in such fashion is about 0.95 in anunpacked state. They are capable of being detonated in a cartridgehaving a diameter of. about 1.25-

inch by a No. 6 Electric Blasting Cap with a detonation velocity ofabout 14,500 ft./sec. The gap sensitivity is a been first briefly groundtogether in amortar in order to disperse the abietic acid throughoutthehexamethylene tetramine. Without this preliminary mixing the abieticacid would tend to coagulate on the surface in the melt.

The mixture therefore consisted of 90 percent by weight ammoniumnitrate, 9 percent by weight hexamethylenetetramine as the primary fueland 1 percent by weight abietic acid as a crystallization modifier.

The mixture in the kettle was continuously stirred with moderate speeduntil a clear melt was formed at a temperature of about 145 C.

The resulting molten mass was then poured into a heated vessel having amultiplicity of small perforations in the bottom. The melt was thenallowed to drip onto a clean, smooth stone table top from a height ofabout two feet while the vessel was moved about in such a Way as todistribute the resulting solidified splattered droplets uniformly overthe surface. This material was then scraped together in a pile by meansof a steel blade and briefly kneaded with glovedhands in order to breakup or granulate the flakes. It was then sifted and rubbed through a 16mesh screen and finally stored in a polyethylene bag. sifting operation,the scraped-up flakes were placed directly in the polyethylene bag andthe granulation accomplished by suitable kneading on the bag.

Due to the hygroscopic nature of ammonium nitrate,

it is important to avoid high ambient humidity (greater than 50 to 60percent relative humidity) and to keep the stored material in a moistureresistant container.

The resulting granulated material when packed into a 1.5 inch steelpipe, 12 inches long, at increasing densities gave the followingmeasured detonation velocities.

Density, gm./cc.: Detonation Velocity, ft./sec.

Explosive formulations may also be made using the adduct of thisinvention in which the fuel is not exclusively hexamethylenetetramine.However, in order to assure a formulation which is sensitive to a No. 6Electric Blasting Cap, the adduct should be present in an amountcorresponding to at least ten percent by weight of the total amount offuel and oxidizer in the formulation. The maximum amount of adduct is,of course, set by that required for oxygen balance with the ammoniumnitrate When no other fuel than the hexamethylenetetramine is used. Inthe latter case, the amount of adduct is about twenty percent by weightof the total amount of fuel and oxidizer in the formulation.Accordingly, the range of effective amount of adduct in a cap sensitiveexplosive formulation is to 20 percent by weight of the total amount offuel and oxidizer in the formulation.

Examples of explosive formulations in which other fuels were used inaddition to hexamethylenetetramine are as follows. A formulation wasmade which consisted of a mixture of 83 percent by weight of ammoniumnitrate, 12.5 percent by Weight of the adduct, and 4.5 percent by weightof wood flour. This formulation was introduced into a 1.25-inch x 8-inchcartridge. Its density was 0.95. It was detonable by a No. 6 ElectricBlasting Cap and had a detonation velocity of 12,300 f./s. Similarly, aformulation was made which consisted of 85.7 percent by weight ofammonium nitrate, 11.7 percent -weight of adduct, and 2.7 percent byweight of finely divided anthracite coal. This second formulation wasalso in rod ced to :1 1254 1. a 5- nc cartridge s d y As an alternativeto the kneading and was 0.95. It, too, was detonable by a No. 6 ElectricBlasting Cap and had a detonation velocity of 11,900 f./s.

Not only may the fuel of the explosive formulations of this invention bein part other than hexamethylenetetramine, but also the oxidizer may inpart be other than ammonium nitrate. Many oxidizers are known in theart. However, even as described above with respect to the partial use ofother fuels, the adduct should be present in an amount between 10 and 20percent by weight of the combined weight of fuel and oxidizer if themaximum cap sensitivity is to be reliably attained.

A natural question is why not simply mix ammonium nitrate andhexamethylenetetramine, instead of resorting to such methods of makingadduct, as presented above. A good blasting explosive formulation can beobtained by using the simple mixture with an adequate primer. However,when packed in cartridge form, 1.25 inches in diameter, the mixture isnot detonated by a No. 6 Electric Blasting Cap and furthermore its gapsensitivity, even when initiated with a tetryl pellet primer, is onlyone inch. For these reasons the simple mixture is not suitabel for useas stick dynamite, although quite useful, as mentioned, in normalblasting operations.

In view of the improved performance resulting from the presence of theabove-described adduct in explosive formulations, I have concluded thatthe improvement results from the pseudo-molecular mixture formed by thefuel and the oxidizer. In other words, the adduct of fuel and oxidizeracts as a molecular explosive, and thereby improves the performance ofany explosive formulation in which it is present.

According to the provisions of the patent statutes, I have explained theprinciple, preferred construction and mode of operation of my inventionand have illustrated and described what I now consider to represent itsbest embodiment. However, I desire to have it understood that, withinthe scope of the appended claims, the invention may be practicedotherwise than as specifically illustrated and described. In particular,it should be understood that other ingredientsconventionally used inexplosive formulations for special purposes may be included in myexplosive formulations.

I claim:

1. The adduct of ammonium nitrate and hexamethylenetetramine in themolar ratio of 2 to 1.

2. The crystalline adduct of ammonium nitrate and hexamethylenetetraminewhich has a melting point of about 122 C. and which has an infraredspectrogram showing characteristic absorption peaks at the followingwave numbers: 868, 1256, 1291, 2490, 2535, 2596, 2625, 2672, 2722, 2790and 2826 cm.- and an X-ray dilfraction pattern with major peaks at 4.07A., 4.45 A., and 5.27 A.

3. The method of making an adduct of ammonium nitrate andhexamethylenetetramine which comprises dissolving said ammonium nitrateand hexamethylenetetramine in water in the molar ratio of about 2 to 1,and removing the water at a temperature below about 40 C. until theadduct is formed.

References Cited in the file of this patent UNITED STATES PATENTS1,720,459 Wyler July 9, 1929 2,345,582 Carey Apr. 4, 1944 2,548,428Fiedorek Apr. 10, 1951 2,579,494 Hermann Dec. 25, 1951

1. THE ADDUCT OF AMMONIUM NITRATE AND HEXAMETHYLENETETRAMINE IN THEMOLAR RATIO OF 2 TO1.
 3. THE METHOD OF MAKING AN ADDUCT OF MAMMONIUMNITRATE AND HEXAMETHYLENETETRAMINE WHICH COMPRISES DISSOLVING SAIDAMMONIUM NITRATE AND HEXAMETHYLENETETRAMINE IN WATER IN THE MOLAR RATIOOF ABOUT 2 TO 1, AND